The liver-secreted protein fibrinogen-like protein 1 (FGL1) is a ligand of the coinhibitory receptor LAG3 on T cells; however, Fgl1-/- mice exhibit autoimmune features distinct from those of Lag3-/- mice. Here, we examined whether FGL1 acts via receptors beyond LAG3 to regulate autoimmunity. Recombinant FGL1 administration reduced autoimmune symptoms in B6/lpr lupus-like mice. This was associated with diminished antigen-specific IgM responses and B cell numbers. Genome-wide surface proteome screening identified the tumor necrosis factor receptor (TNFR) family member transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), a receptor for B cell-activating receptors BAFF and APRIL, as a receptor for FGL1. TACI bound FGL1 via an N-terminal site not required for BAFF and APRIL interaction. The impact of FGL1 administration on B cell numbers and autoimmune phenotypes was lost in Taci-/- mice. Mechanistically, FGL1 promotes TACI internalization, thereby regulating receptor availability for activating ligands. Thus, FGL1 regulates an innate-like subset of B cells via modulating TACI availability, with implications for autoimmunity and inflammation.

B-cell maturation antigen (BCMA) targeting gained a rapid approval for multiple myeloma, and is currently investigated in B-cell lymphomas. Here, we report that the trans Golgi network (TGN) retained BCMA due to a motif in its transmembrane/cytoplasmic domain in diffuse large B-cell lymphomas (DLBCL). To achieve signaling, one of its ligands, a proliferation inducing ligand (APRIL), bound to surface heparan sulfate proteoglycans (HSPGs), got endocytosed by the calveolin pathway and trafficked to the TGN via the retrograde route. In the TGN, APRIL/BCMA interactions activated the NF-κB pathway. BCMA ubiquitination followed by proteosomal degradation mediated signal termination. Growth impairment of DLBCL xenografts in APRIL -deficient animals confirmed the in vivo activity of TGN BCMA. Our study constitutes the first description for a signal activity from the Golgi apparatus among the TNF receptor family. ### Competing Interest Statement The authors have declared no competing interest. La Ligue Contre le Cancer, https://ror.org/00rkrv905 region auvergen rhône-alpes feder

Lesions in the CNS are frequently associated to a detrimental inflammatory reaction. In autoimmune neurodegenerative diseases, a proliferation-inducing ligand (APRIL) produced by CNS-infiltrating inflammatory cells binds to chondroitin sulphate proteoglycans (CSPGs). The latter are well-established obstacles to neural regeneration and remyelination in the CNS by interacting with receptor protein tyrosine phosphatase (RPTP) and Nogo receptor (NgR) families. Here, we are showing that APRIL blocks the interactions of RPTP and NgR with all types of chondroitin sulphate (CS). Functionally, APRIL neutralized the inhibitory effects of CS on mouse and human neuronal process growth. APRIL also blocked the inhibition of CS on mouse and human oligodendrocyte differentiation. Finally, APRIL increased myelination in an ex vivo organotypic model of demyelination in the presence of endogenous CSPG upregulation. Our data demonstrate the potential value for a recombinant form of soluble APRIL to achieve repair in the CNS.

Durable responses to currently available CAR T cell therapies for relapsed or refractory multiple myeloma (R/R MM) are limited in part by BCMA antigen escape and immunologic responses to the CAR construct. Moreover, effective therapies for patients (pts) who progress after receiving BCMA CAR T cells in R/R MM remain an unmet need. TriPRIL CAR T cells were developed to co-target BCMA and TACI using a trimeric form of their natural ligand APRIL, fused to the 4-1BB and CD3ζ intracellular signaling domains. Targeting multiple antigens using a single ligand-based CAR may minimize antigen-negative tumor escape and immune responses to the construct. We present both clinical and translational correlative studies from an ongoing, first-in-human, phase 1 clinical trial of autologous TriPRIL CAR T cells in pts with R/R MM (# NCT05020444). Eligible pts with R/R MM had received at least 3 prior lines of therapy or had triple class-refractory disease. Prior BCMA-targeting therapy was allowed. The primary endpoint was incidence of dose-limiting toxicities (DLTs) and adverse events. The study employed a 3+3 dose escalation design followed by dose expansion. If the target CAR T cell dose was not manufactured, pts could receive infusion at the lower dose level. TriPRIL CAR T cells were evaluated using flow cytometry and vector copy number. BCMA and TACI expression were assessed by flow cytometry on bone marrow plasma cells before and after infusion. To further explore the mechanisms of response and resistance, ex vivo CAR-T function, as well as soluble BCMA, TACI, APRIL, and BAFF, were evaluated. As of July 9, 2025, 11 pts had undergone leukapheresis and 10 pts had received TriPRIL CAR T infusion. Five pts were treated at dose level 1 (1 x10^8 CAR T cells) and 5 pts at dose level 2 (3 x10^8 CAR T cells). Among the infused pts, the median age was 73 years (range 62-82), and 8 pts were female (80%). Pts had received a median of 6 prior lines of therapy (range, 3-10). Six pts (60%) had received previous BCMA CAR T therapy. Six pts (60%) had high-risk cytogenetics, and 3 pts (30%) had extramedullary disease. No DLTs occurred at either dose level. Grade 1 or 2 CRS occurred in all pts (100%; Grade 1: 80%, Grade 2: 20%). One patient (10%) had Grade 2 ICANS. There were no Grade 3 or higher CRS or ICANS events, nor occurrences of Parkinsonism or cranial nerve palsies. The median follow-up time among pts who remain alive is 11.9 months (mo). The overall response rate (ORR) was 80% with a complete response (CR) rate of 60%. Four of the 6 pts (67%) who previously received BCMA CAR T cells achieved a CR. The median PFS was 8.4 mo (95% CI, 0.9-11.1) among the entire cohort and 8.4 mo (95% CI, 0.9-NE) among pts with prior BCMA CAR T. One patient with prior BCMA CAR T therapy was in an ongoing CR 14 mo post-TRiPRIL infusion. The median OS had not been reached (95% CI, 3.8-NE). CAR T expansion occurred in all pts (median peak expansion 2713 cells/μl blood), with persistence beyond mo 3 in 9 pts (90%). All 5 pts in remission at mo 6 had ongoing CAR T persistence at this timepoint. In contrast, one patient who did not respond had limited expansion (6 cells/μl blood), and CAR T cells did not persist beyond day 21. The only other non-responder had BCMA and TACI-negative plasma cells pre-infusion, having previously received BCMA CAR T therapy. Circulating CAR T cells from this patient remained functional, killing a BCMA-positive cell line ex vivo (RPMI-8226). Further correlative studies of bone marrow plasma found that soluble BCMA and TACI declined from baseline to D+28 post-infusion, in keeping with the destruction of target antigen. In contrast, soluble BAFF and APRIL increased. Furthermore, we identified soluble TriPRIL in the serum of responding pts post-infusion, which corresponded to peak CAR T cell expansion. TriPRIL CAR T cells demonstrated notable safety and a high response rate in heavily pretreated pts with R/R MM, including pts who previously received BCMA CAR T. TriPRIL is one of the first ligand-based CAR T cell therapies to show efficacy in an early phase clinical trial. Correlative studies demonstrated potential mechanisms of resistance, including the absence of both target antigens and a lack of sustained CAR T cell expansion in a patient recently treated with a bispecific antibody. Our findings support and inform the continued clinical development of TriPRIL CAR T cells. Updated data through November 2025 will be presented.

The TNF family member LIGHT (TNFSF14) binds to two receptors, HVEM (TNFSFR14) and LTβR (TNFSFR3). HVEM functions as a costimulatory molecule, whereas LTβR is involved in the development of lymph nodes and ectopic tertiary lymphoid structures at chronic inflammation sites. The classical approach of fusing soluble recombinant proteins to the Fc fragment of IgG resulted in a functionally inactive Ig.mouse (m) LIGHT protein. However, in line with the fact that TNF family members cluster receptors as trimers, addition of a small homotrimeric domain (foldon) N-terminal of mLIGHT produced an Ig.Foldon-mLIGHT protein able to bind and engage HVEM and LTβR in a cell-based reporter bioassay. In the tumor model of B16.F10 melanoma cells implanted into syngeneic recipients, cells transduced with membrane-bound mLIGHT grew as aggressively as mock-transduced cells, but growth of tumors of B16.F10 cells expressing Ig.Foldon-mLIGHT was delayed and characterized by significant immune infiltration of dendritic cells and cytotoxic cells. This work unveils the potential of active soluble LIGHT, as a single agent, to recruit cytotoxic cells and dendritic cells at the tumor site to inhibit tumor growth. This effect may be further enhanced with immune checkpoint blockade therapies. KEY MESSAGES: The classical approach of fusing soluble recombinant proteins to the Fc fragment of IgG resulted in a functionally inactive Ig.mouse (m) LIGHT (TNFSF14) protein. The addition of a small homotrimeric domain (foldon) N-terminal of mouse LIGHT produces a proper folded bioactive mouse LIGHT recombinant protein. Constitutive intratumor expression of secreted Ig-Foldon-LIGHT, but not membrane LIGHT, delays tumor growth. Tumors secreting LIGHT, as a single agent, promote beneficial anti-tumor responses through the recruitment and infiltration of cytotoxic cells and dendritic cells.

Although liver kinase B1 (LKB1) has been established as a tumor suppressor kinase, its mechanism of action is incompletely understood. Here we describe a novel nonenzymatic function of LKB1 in cell death induced by Fas/CD95. In BID knockout HeLa cells, inactivation of mitochondrial outer membrane permeabilization (MOMP) prevents Smac-induced inhibition of X-linked inhibitor of apoptosis (XIAP), causing resistance to Fas-induced apoptosis. However, reexpression of LKB1 in those cells naturally deficient for endogenous LKB1 restored apoptosis. Mechanistically, caspase-8 activated by Fas processed LKB1 to a truncated form, tLKB1. Both WT and kinase-inactive LKB1 antagonized XIAP to restore apoptosis, but somatic mutants of LKB1 found in Peutz-Jeghers syndrome (PJS) failed to do so. Thus, in addition to the known caspase-8 / tBid / Smac / XIAP pro-apoptotic axis, our results unveil a novel one, caspase-8 / tLKB1 / XIAP that potentially contributes to the antitumor functions of LKB1.

Defective FAS (CD95/Apo-1/TNFRSF6) signaling causes autoimmune lymphoproliferative syndrome (ALPS). Hypergammaglobulinemia is a common feature in ALPS with FAS mutations (ALPS-FAS), but paradoxically, fewer conventional memory cells differentiate from FAS-expressing germinal center (GC) B cells. Resistance to FAS-induced apoptosis does not explain this phenotype. We tested the hypothesis that defective non-apoptotic FAS signaling may contribute to impaired B cell differentiation in ALPS. We analyzed secondary lymphoid organs of patients with ALPS-FAS and found low numbers of memory B cells, fewer GC B cells, and an expanded extrafollicular (EF) B cell response. Enhanced mTOR activity has been shown to favor EF versus GC fate decision, and we found enhanced PI3K/mTOR and BCR signaling in ALPS-FAS splenic B cells. Modeling initial T-dependent B cell activation with CD40L in vitro, we showed that FAS competent cells with transient FAS ligation showed specifically decreased mTOR axis activation without apoptosis. Mechanistically, transient FAS engagement with involvement of caspase-8 induced nuclear exclusion of PTEN, leading to mTOR inhibition. In addition, FASL-dependent PTEN nuclear exclusion and mTOR modulation were defective in patients with ALPS-FAS. In the early phase of activation, FAS stimulation promoted expression of genes related to GC initiation at the expense of processes related to the EF response. Hence, our data suggest that non-apoptotic FAS signaling acts as molecular switch between EF versus GC fate decisions via regulation of the mTOR axis and transcription. The defect of this modulatory circuit may explain the observed hypergammaglobulinemia and low memory B cell numbers in ALPS.

Helicobacter infection is a key cause of gastric B cell mucosa-associated lymphoid tissue (MALT) lymphoma. This study examined the role of B cell-activating factor (BAFF), a major driver of B cell proliferation and many B cell disorders, in this malignancy using a model in which conditional knockout mice for NOD-like receptor family CARD domain-containing 5 (Nlrc5) are infected with Helicobacter felis. Gastric BAFF production was significantly increased in H. felis-infected Nlrc5mø-KO mice compared to wild-type. Blocking BAFF signalling, before or after the onset of Helicobacter-induced gastritis, significantly reduced MALT development, with fewer gastric B cell follicles and reduced gland hyperplasia. BAFF blockade also reshaped the immune cell landscape in the stomach, resulting in fewer CD4+ T cells, Tregs, macrophages and dendritic cells. Using a cell culture model, we identified the protein-coding BAFF transcripts that are upregulated in NLRC5-deficient macrophages stimulated with either H. felis or the NLRC5 agonist, lipopolysaccharide. Among the upregulated variants, TNFSF13B (BAFF)-206 acts as a transcription factor and is reported to enhance BAFF production in autoimmune diseases and cancer. Altogether, these findings implicate the NLRC5-BAFF signalling axis in Helicobacter-induced B cell MALT lymphoma, highlighting BAFF inhibition as a potential therapeutic approach.

BackgroundChronic Lymphocytic Leukemia (CLL) is characterized by the expansion of CD19+ CD5+ B cells but its origin remains debated. Mutated CLL may originate from post-germinal center B cells and unmutated CLL from CD5+ mature B cell precursors. Irrespective of precursor types, events initiating CLL remain unknown. The cytokines BAFF and APRIL each play a significant role in CLL cell survival and accumulation, but their involvement in disease initiation remains unclear.MethodsWe generated novel CLL models lacking BAFF or APRIL. In vivo experiments were conducted to explore the impact of BAFF or APRIL loss on leukemia initiation, progression, and dissemination. Additionally, RNA-seq and quantitative real-time PCR were performed to unveil the transcriptomic signature influenced by BAFF in CLL. The direct role of BAFF in controlling the expression of tumor-promoting genes was further assessed in patient-derived primary CLL cells ex-vivo.ResultsOur findings demonstrate a crucial role for BAFF, but not APRIL, in the initiation and dissemination of CLL cells. In the absence of BAFF or its receptor BAFF-R, the TCL1 transgene only increases CLL cell numbers in the peritoneal cavity, without dissemination into the periphery. While BAFF binding to BAFF-R is dispensable for peritoneal CLL cell survival, it is necessary to activate a tumor-promoting gene program, potentially linked to CLL initiation and progression. This direct role of BAFF in controlling the expression of tumor-promoting genes was confirmed in patient-derived primary CLL cells ex-vivo.ConclusionsOur study, involving both mouse and human CLL cells, suggests that BAFF might initiate CLL through mechanisms independent of cell survival. Combining current CLL therapies with BAFF inhibition could offer a dual benefit by reducing peripheral tumor burden and suppressing transformed CLL cell output.

Antibody-producing plasma cells fuel humoral immune responses. They also contribute to autoimmune diseases such as systemic lupus erythematosus or IgA nephropathy. Interleukin-6 and the tumor necrosis factor (TNF) family ligands BAFF (B cell-activating factor) and APRIL (a proliferation-inducing ligand) participate in plasma cell survival. BAFF binds to three receptors, BAFFR (BAFF receptor), TACI (transmembrane activator and CAML interactor), and BCMA (B cell maturation antigen), while APRIL binds to TACI, BCMA, and proteoglycans. However, which ligand–receptor pair(s) are required to maintain plasma cells in different body locations remains unknown. Here, by combining mouse genetic and pharmacological approaches, we found that plasma cells required BCMA and/or TACI but not BAFFR. BCMA responded exclusively to APRIL, while TACI responded to both BAFF and APRIL, identifying three self-sufficient ligand–receptor pairs for plasma cell maintenance: BAFF–TACI, APRIL–TACI, and APRIL–BCMA. Together, these actors accounted for 90% of circulating antibodies. In BAFF-ko mice, the reduction of plasma cells upon APRIL inhibition indicated that APRIL could function in the absence of BAFF–APRIL heteromers. No evidence was found that in the absence of BCMA and TACI, binding of APRIL to proteoglycans would help maintain plasma cells. IL-6, alone or together with BAFF and APRIL, supported mainly splenic plasmablasts and plasma cells and contributed to circulating IgG but not IgA levels. In conclusion, survival factors for plasma cells can vary with body location and with the antibody isotype that plasma cells produce. To efficiently target plasma cells, in particular IgA-producing ones, dual inhibition of BAFF and APRIL is required.

Introduction The therapeutic interest of targeting B-cell activating factor (BAFF) in Sjögren’s disease (SjD) can be suspected from the results of two phase II clinical trials but has not been evaluated in an animal model of the disease. We aimed to evaluate the therapeutic efficacy of this strategy on dryness and salivary gland (SG) infiltrates in the NOD mouse model of SjD.Material and methods Female NOD mice between ages 10 and 18 weeks were treated with a BAFF-blocking monoclonal antibody, Sandy-2 or an isotype control. Dryness was measured by the stimulated salivary flow. Salivary lymphocytic infiltrates were assessed by immunohistochemistry. Blood, SGs, spleen and lymph-node lymphocyte subpopulations were analysed by flow cytometry. SG mRNA expression was analysed by transcriptomic analysis.Results BAFF inhibition significantly decreased SG lymphocytic infiltrates, which was inversely correlated with salivary flow. The treatment markedly decreased B-cell number in SGs, blood, lymph nodes and spleen and increased Foxp3+ regulatory and CD3+CD4−CD8− double negative T-cell numbers in SGs.Conclusion A monoclonal antibody blocking BAFF and depleting B cells had therapeutic effectiveness in the NOD mouse model of SjD. The increase in regulatory T-lymphocyte populations might underlie the efficacy of this treatment.

PDF file - 184K, (A) The RANKL antibodies MIH23 and MIH24 specifically bind to RANKL. Binding of MIH23 and MIH24 to surface expressed RANKL was determined by FACS using RANKL transfectants (L-RANKL) and control cells (L cells). Shaded peaks, specific mAb (MIH23 and MIH24); open peaks, isotype controls (mouse IgM and mouse IgG2b, respectively). (B) MIH23 and MIH24 block RANK-RANKL interaction. RANKL transfectants and the parental controls were stained with RANK-Ig (shaded peaks) or human IgG1 (open peaks) followed by anti-human-PE and investigated by FACS. Dotted line: staining after preincubation with the indicated RANKL mAb; dashed line: after preincubation with mouse IgM and mouse IgG2b as respective isotype controls. (C) Sensitivity and specificity of the sandwich ELISA for detection of sRANKL. The indicated serial dilutions of rRANKL in culture medium were analyzed as described in the methods section. X represents 100ng/ml rGITRL as control. The dotted line represents the chosen detection limit of 0.05ng/ml. Means of triplicates with standard deviations are shown. (D, E) MM cell lines do not display RANKL protein on the surface despite expression of mRANKL mRNA. The indicated MM cell lines were analyzed for RANKL surface and mRNA expression by FACS (D) and RT-PCR (E) as described in the methods section. Results obtained with RANKL transfectants and parental cells are shown as controls.

<p>APRIL-producing neutrophils infiltrate the tumor nest.</p>

X-linked hypohidrotic ectodermal dysplasia (XLHED), caused by a genetic deficiency of ectodysplasin A1 (EDA1), is a rare developmental disorder of ectodermal derivatives such as hair, sweat glands, and teeth. The absence of sweat glands and perspiration can evoke life-threatening hyperthermia. As molecular genetic findings are not always conclusive, the concentrations of circulating EDA1 may help to distinguish between total and partial EDA1 deficiencies. We previously treated nine male patients with obvious signs of XLHED with a recombinant EDA1 replacement protein, Fc-EDA, either shortly after birth (n = 3) or by prenatal administration in gestational week 26 and beyond (n = 6). Here, we present the long-term follow-up for up to six years. In patients who had received Fc-EDA after birth, neither sweat glands nor sweating ability were detected at the age of 12–60 months. In contrast, prenatal EDA1 replacement resulted in ample sweat gland development and pilocarpine-inducible sweating in all treated subjects, who also attained more permanent teeth than their untreated affected relatives. Normal perspiration has persisted for six years in the two oldest boys treated repeatedly with Fc-EDA in utero. When they had a sauna, adequate thermoregulation was evidenced. Lower sweat production after single prenatal dosing may indicate a dose–response relationship. The absence of circulating EDA1 in five prenatally treated subjects proved that these children would have been unable to perspire if they had been left untreated. The sixth infant was shown to produce an EDA1 molecule that, albeit interacting with its cognate receptor, cannot activate EDA1 signaling. In conclusion, a causal treatment of XLHED before birth is feasible.

PDF file - 264K, (A) The ability of MM cells to release sRANKL does not influence NK reactivity induced by RANK-Fc-ADCC. The increase in cytotoxicity (left) and cytokine production (right) of allogeneic NK cells using RANKL surface-positive MM cells that do (+sRANKL) or do not (-sRANKL) release sRANKL as targets upon treatment with RANK-Fc-ADCC was calculated. To this end, specific lysis (E:T ratio 40:1) or cytokine release (E:T ratio 1:1) of NK cells in the presence of isotyp control-treated target cells was set to 1 in each individual data set. No statistically significant difference (p=0.39 and p=1, respectively; Mann-Whitney U-Test) was observed upon analysis of results from 8 (cytotoxicity) and 6 (cytokine release) independent experiments. (B) Surface levels of RANKL do not correlate with induction of NK reactivity by RANK-Fc-ADCC. Expression of RANKL on patient MM (circles) and CLL cells (triangles) was correlated with the increase in cytotoxicity (left) and cytokine production (right) of allogeneic NK cells upon treatment with RANK-Fc-ADCC calculated by as described in A. Each symbol represents the result of one independent experiment. The number of independent experiments, correlation coefficients (Pearson correlation) and p values (T-Test) are indicated. (C) NK reactivity against RANKL surface-negative MM cells is not affected by the fusion proteins. RPMI 8226 MM cells (left) and primary MM cells (right) that lack RANKL surface expression were incubated with allogeneic NK cells in the presence or absence of 10mug/ml of the indicated RANK fusion proteins or isotype control. Cytotoxicity was determined by 2h Europium release assays (upper panels) and IFN-gamma levels in supernatants were analyzed after 24h by ELISA (lower panels). (D) RANKL transfectants were cultured with allogeneic NK cells in the presence or absence of RANK-Fc-ADCC or isotype control (10g/ml each) and the indicated concentrations of rRANKL. Cytotoxicity was determined by 2h Europium release assays (left) and IFN- levels in supernatants were analyzed after 24h by ELISA (right). One repesentative experiment each of a total of three with similar results is shown in C and D.